Cable television (CATV) is a form of broadcasting that transmits programs to paying subscribers via a physical land based infrastructure of coaxial (“coax”) cables or via a combination of fiber-optic and coaxial cables (HFC).
CATV networks provide a direct link from a transmission center, such as a head-end, to a plurality of subscribers at various remote locations, such as homes and businesses, which are usually stationary and uniquely addressable. The head-end may be connected to the subscribers via local hubs, commonly referred to as “nodes”, which route the flow of data to and/or from a predefined group of subscribers, e.g., hundreds of subscribers, in a defined geographical area, for example, a small neighborhood or an apartment complex. The typical distances between the local nodes and the subscribers are relatively short, for example, up to a few thousand feet. Therefore, the communication between nodes and their subscribers is commonly referred to as “last mile” communication.
Existing CATV networks utilize a signal distribution service to communicate over multiple channels using various formats, for example, analog and/or digital formats for multi-channel TV programs, a high definition TV (HDTV) format, providing interactive services such as “video on demand”, and other multimedia services, such as Internet access, telephony and more.
A number of elements are involved in maintaining a desired flow of data through coaxial conductors or through a combination of fiber optics and coaxial cables from the head-end to the subscribers of a CATV system. In a conventional HFC cable TV system, the head end is connected to the local nodes via dedicated optical fibers. In the last mile system, each local node converts the optical signals received from the head-end into corresponding electrical signals, which may be modulated over a radio frequency (RF) carrier, to be routed to the local subscribers via coax cables.
The head-end is the central transmission center of the CATV system, providing content (e.g., programs) as well as controlling and distributing other information, e.g., billing information, related to customer subscribers.
The downstream signals, which are limited to designated channels within a standard frequency range (band) of 48 MHz to 860 MHz (or up to 1,000 MHz by recently introduced Stretching technology) are modulated on a light beam, e.g., at a standard wavelength of 1550 nm, and sent to the local node via a fiber-optical cable. An optical converter at the local node detects the optical signals and converts them into corresponding electrical signals to be routed to the subscribers.
In the reverse direction, the local optical node receives upstream data from all the local subscribers in the last mile section. These are carried by RF electrical signals at a standard frequency band of 5 MHz to 42 MHz, which does not overlap with the downstream band. A converter in the local optical node converts the upstream data into corresponding optical signals by modulating the data on an optical carrier beam, e.g., at a wavelength of 1310 nm, to be transmitted back to the head-end.
The electrical last mile system usually includes low-loss coax cables, which feed a plurality of serially-connected active elements, for example, line extension amplifiers and, if necessary, bridge trunk amplifiers (e.g., in case of splitting paths). In addition, many passive devices of various types may be fed by tapping from the main coaxial line in between the active amplifiers. These passive devices may be designed to equalize the energies fed to different subscriber allocations such that signals allocated to subscribers closer to the local node and/or to one or more of the active devices may be attenuated more than signals allocated to subscribers further away from the node or active devices.
In conventional systems, each passive device can feed a small group of subscribers, usually up to 8 subscribers, via drop cables having a predetermined resistance (e.g., 75Ω), feeding designated CATV outlets at the subscriber end. The drop cables are flexible and differ in attenuation parameters from the coaxial cables that feed the passive devices. The hierarchy of commonly used coaxial drop cables includes the RG-11 coaxial cable, which has the lowest loss and thus the highest performance, then the intermediate quality RG6-cable, and finally the basic quality RG-59 cable. All drop cables used in the industry are usually connected using standard “F type” connectors.